Method and System for Monitoring Steam Quality

ABSTRACT

A method and apparatus for monitoring the quality of steam used in a process is disclosed. A pressure and temperature sensor is exposed to the steam on either side of an inline pressure drop device such as an orifice or pressure reducing valve. The measurements are transmitted to a controller that calculates the steam quality percentage or superheat value. An alarm is issued if the steam quality is beyond a predetermined tolerance.

FIELD OF THE INVENTION

The present invention relates generally to steam control systems, andmore particularly to a method and system for monitoring the qualityand/or purity of steam used in a decontamination system such as a steamsterilizer or a steam injection device for pharmaceutical or foodprocessing.

BACKGROUND OF THE INVENTION

Steam has been used in decontamination systems, such as sterilizers orautoclaves located in hospitals, manufacturing settings, andlaboratories to sterilize devices such as medical and dentalinstruments, laboratory instruments, production equipment, manufacturedproducts, and other articles. Steam is also used for vulcanizing,cooking, melting, humidifying, and drying in process industries such aspharmaceuticals, foods, paper, automotive, and printing, etc.

Steam purity and steam quality are important properties of steam thatwill affect the efficacy of a decontamination process, such as steamsterilization. Steam purity is an expression of the quantity ofnon-water components (vaporous contamination) carried in the steam.Steam quality refers to the quantity of moisture present in the steam.If there is no moisture (i.e., no liquid water), then the steam is of100% quality. Accordingly, “pure” steam has a liquid water content of0%. It should be appreciated that steam quality relates to steam puritybecause liquid droplets in steam may contain dissolved solids that maybe transmitted to the process.

In many healthcare and pharmaceutical applications, the minimumacceptable steam quality for a steam sterilizer or autoclave is 95%. Ifsteam quality is below 95%, then “wet packs” (i.e., moisture droplets)may develop on articles after completion of a sterilization cycle.Consequently, reprocessing will be required, and/or batches of productmay have to be discarded.

Aside from decontamination, many processes require steam that is dry andcontains no superheat. Printing presses use steam to control staticelectricity and to precisely control the drying and shrinkage of thepaper. Poor steam quality can upset the control. Wet steam can evencause the paper to tear, ruining a press run. Dairy applications injectsteam directly into milk during pasteurization. Wet steam can carrycontaminants and add too much water during the injection process.

A steam generator used to vaporize water can introduce contaminants intothe steam, thereby reducing steam purity. For example, where the steamgenerator is a boiler, boiler chemicals can be introduced into the steamduring priming or foaming of the boiler. These contaminants may causecorrosion or staining of the product or decontamination device (e.g.,steam sterilizer) or articles to be processed by exposure to the steam.

Attempts have been made to check the quality of steam in an effort toreduce some of the problems caused by steam with an inappropriatequality. U.S. Pat. No. 4,561,785 issued to Long claims to disclose a“method and apparatus for determining the quality of typical steam usedin steam flooding for secondary recovery of petroleum” by continuouslyleaking a portion of high-pressure steam out of the system. Althoughleaking hot steam out of a system may be acceptable for oil well fields,there are many situations where such a hazard is not acceptable.

Other methods of analysis have been attempted such as in U.S. Pat. No.4,547,078 issued to Long where steam quality is measured at a specificpoint in time by “obtaining a sample of the liquid component of steamand determining the quality of steam in a vessel or the like, such assteam flowing in a line used for steam injection in an oil well. Thesteam quality is determined by the known method of comparing theconcentrations of dissolved solids in the liquid sample and thefeedwater.”

These steam quality measurements are time consuming, inaccurate, and canexpose operators to potentially unsafe conditions including scaldingheat and deafening noise. Moreover, other approaches to measuring steamquality do not provide advanced warnings of problems with quality of thesteam used in a process.

SUMMARY OF THE INVENTION

A method and system for monitoring the quality steam used in a processis disclosed. A pressure and temperature sensor is exposed to the steamon either side of a pressure drop device such as an orifice or pressurereducing valve. Pressure and temperature sensors are exposed to thesteam on either side of a pressure drop. The measurements aretransmitted to a controller that continuously calculates the steamquality or superheat value and issues an alarm if the steam quality isbeyond a predetermined tolerance.

The foregoing summary does not limit the invention, which is defined bythe attached claims. Similarly, neither the Title nor the Abstract is tobe taken as limiting in any way the scope of the disclosed invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Each of the drawing figures now described shows an exemplary embodimentof the present invention.

FIG. 1 is a side view of a steam pressure reducing station with inlinesteam testing of steam being delivered to a sterilization chamber.

FIG. 2 is a schematic diagram of a sensor circuit for inline continuousmonitoring of steam quality and superheat, the circuit having bothpressure and temperature sensors upstream and downstream of a pressurereducing device.

FIG. 3 is a schematic diagram of a sensor circuit for monitoring steamquality and superheat by sensing both the pressure and temperatureupstream and downstream of a process control valve.

FIG. 4 is a schematic diagram of a sensor circuit for monitoring steamquality and superheat by sensing both the pressure and temperatureupstream and downstream of an orifice plate.

FIG. 5 shows a steam quality calculator continuously monitoring thequality of steam passing through a pressure reducing station

FIG. 6 is a schematic diagram of a steam system testing the steamquality of high, medium, and low pressure steam.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings wherein the showings are for the purposeof illustrating the preferred embodiments. FIG. 1 shows a steam system10 having a first temperature sensor 300, a first pressure sensor 400, asecond temperature sensor 500, and a second pressure sensor 600 flankingan inline pressure reducing valve 22 for monitoring the purity and/orquality of steam used within the system. An “inline pressure reducer” isherein defined to be a mechanism structured to reduce the pressure of agas to a pressure above atmospheric pressure, wherein the reducedpressure gas is provided to a device that performs a function other thangas analysis. In the illustrated embodiment, system 10 is a steamsterilization system for cleaning articles with steam. It should beunderstood that while a preferred embodiment of the present invention isdescribed with reference to a steam sterilization system, it iscontemplated that the present invention may be used in connection withother systems and facilities that utilize steam.

The steam sterilization system 10 generally comprises a vessel 30, anouter jacket 40, a steam generator 50, a control unit 60, and the firsttemperature sensor 300. The vessel 30 defines a chamber 32 that may beany shape, but is preferably cylindrical or rectangular. Articles to besterilized are placed into chamber 32 for exposure to steam.

Steam is released from chamber 32 through an outlet conduit 16. A steamoutlet valve 26 controls the release of steam from the chamber 32.

The outer jacket 40 surrounds vessel 30 and defines a steam region 42between the vessel 30 and the outer jacket 40 for injection of steam.Like the vessel, the outer jacket 40 is preferably cylindrical orrectangular in shape. An input conduit 14 connects the steam region 42with the chamber 32. A steam control valve 24 regulates the flow ofsteam between the steam region 42 and the chamber 32.

The steam generator 50 may produce steam through a variety of differentheating methods. For example, the steam generator 50 may include aconventional natural gas boiler, an electrically powered resistiveheating element, or the output of a high efficiency heat pump system.Water is supplied to a steam generator 50 through a water input conduit18. Steam produced by the steam generator 50 is supplied to the steamregion 42 by a first conduit 12. A sterilization valve 24 regulates theflow of steam into and out of the steam region 42. Steam may beintermittently provided to the sterilization unit in order to allowoperators to add or remove surgical instruments from the sterilizationunit without being scalded by steam. While the steam is flowing to thesterilization unit, and when the steam is stagnant, the temperature andpressure sensors may continuously provide updates on the quality of thesteam. In one embodiment of the system, steam is provided to thesterilization unit for at least five minutes (and preferably 20 minutes)before the sterilization unit is isolated from the steam.

The control unit 60 is preferably a microprocessor or a microcontrollerprogrammed on a computer readable medium to control operation of thesystem 10. In this regard, the control unit 60 sends control signals tooperate valves 22, 24 and 26.

The temperature sensors (300 & 500) and the pressure sensors (400 & 600)may take the form of any suitable sensing device responsive to changesin the pressure and temperature of steam used within the system 10. InFIG. 1, the temperature sensors are shown to be upstream of the pressuresensors, however temperature sensors may also be located downstream orparallel with the pressure sensors. Also, both pressure sensors may bebetween the temperature sensors and vice versa. Exemplary pressuresensors are shown flanking a pressure reducing reduction device 62 inFIG. 2 and exemplary temperature sensors are shown around a processcontrol valve 64 in FIG. 3. In FIG. 4, sensors are located upstream anddownstream of an orifice plate 66. In FIGS. 2 and 3, all of the steammixture in the high pressure region passes through the inline pressurereducers.

The sensors 300, 400, 500, and 600 allow the control unit 60 tocontinuously compute and display (a) an indicator showing whether thesteam is superheated or saturated; and (b) a second indicator showingthe degree of superheat or the percentage of steam quality, also knownas the dryness fraction.

The sensors 300, 400, 500, and 600 are preferably located near adedicated pressure reducing valve 22, but it is also contemplated thatthey could be located in alternative locations with steam pressuredifferentials such as the steam control valve 24. Furthermore, it iscontemplated that multiple control units could be included in system 10,to allow for monitoring of steam purity and/or steam quality at severallocations therein. Alternatively, one control unit could calculate steamquality at a plurality of different locations having a plurality ofdifferent steam pressures and temperatures.

Physical properties of steam are stored on a computer readable medium inthe control unit 60. Data tables or algorithms to compute steam qualityand superheat are then used during the processing function to calculatesteam quality and/or the degree of superheat. In this regard, it shouldbe appreciated that the calculation required revolves around themeasured pressure and temperature versus the known physical properties.Thus if 30 psia is measured by the pressure sensor downstream of thepressure reducing valve 22, but only 240° F. temperature is indicated bythe temperature sensor downstream, then the steam quality is below 100%.The resulting quality percentage can be displayed, communicated as analarm condition, or otherwise used for control of the process. Theintroduction of impurities (i.e., vaporous contaminants) into the steamwill cause both the upstream and downstream conditions of the steam tochange. For example, the introduction of air or carbon dioxide willresult in changes to the steam temperature, but not the steam pressure.The presence of condensed water in the steam will generally cause adecrease in upstream temperature but not always, since the water can beat the saturation temperature. The presence of liquid water upstreamwill cause a drop in the temperature downstream. Accordingly, thecontrol unit 60 can be used to ascertain a measure of steam purityand/or steam quality.

FIG. 5 illustrates an example of a steam quality calculator 72continuously monitoring the quality of steam passing through a pressurereducing station. Thermocouples 74 and diaphragm gauges 76 for measuringpressure are located upstream and downstream of an inline steam pressurereducer 78. Isolation valves 80 are located upstream and downstream ofboth the pressure reducer and the pressure and temperature gauges. Inthe event that the steam quality drops below an acceptable threshold,the isolation valves may be utilized to stop the flow of steam throughthe pressure reducing station. A strainer 82 is located proximal to thepressure reducer 78 for removing steam condensate from the line. Abypass line 84 may be connected before and after the isolation valves toallow high pressure steam to be delivered downstream of the pressurereducer if desired. In the bypass line an isolation valve 86 selectivelyallows steam to flow through the isolation line.

FIG. 6 illustrates an example of a steam system delivering highpressure, medium pressure, and low pressure steam to three differentdevices requiring three separate pressures of steam. A steam generator50 provides high pressure steam (80-100 psi) to a high pressure steamartery 90. In passing through a inline process control valve 64 thepressure of the steam is reduced to a medium pressure (50-60 psi) in amedium pressure steam artery 92. A second inline process control valve64 further reduces the pressure of the steam being provided to a lowpressure steam artery 94, typically 10-15 psi. From the high pressuresteam artery 90, a portion of the steam is diverted through a inlinepressure reducer 62 to a first pressure line 96 connecting to a highpressure device 104 such as a washing or ironing machine. A portion ofthe steam from the medium pressure line is also diverted, and passesthrough a pressure reducer 62 to a second pressure line 98 connecting toa medium pressure device 106 such as a cleaning device for a kitchen.Finally, steam from the low pressure artery 94 passes through a thirdpressure reducer 62 to a third pressure line 100. Steam in the thirdpressure line is delivered to a low pressure steam device 108 such as awater heater, humidifier, or air handling unit coils. In addition toissuing warnings if the steam quality falls below a predeterminedthreshold, the steam system may control a desuperheating device todecrease the temperature of the steam if the temperature is above thesteam saturation threshold for a given pressure. In an exemplaryembodiment of the invention, all of the features shown in FIG. 6 may beenclosed with a single hospital building. In another embodiment, thesteam has a pressure of 50-100 psig in the high region pressure regionthat drops to 25-35 psig in the low pressure region. In anotherexemplary system, the steam pressure drops from 60 psig in the highpressure region to 30 psig in the low pressure region.

A control unit (not shown) monitors and stores data signals from theplurality of pressure and temperature sensors (300, 400, 500, and 600)located upstream and downstream of the inline pressure reducers. Usingthe pressure and temperature data, the control unit is able to calculatethe superheat and steam quality of the steam passing through the system.In the event that the steam quality provided to the devices falls belowan acceptable range, the control unit 60 may close off the inlinepressure reducers and isolate a selected number of devices.Alternatively, each pressure drop may have an independent analysismodule with pressure sensors, temperature sensors, steam qualitycalculators, and alarms. The acceptable ranges of steam quality for thehigh-pressure device 104, the medium pressure device 106, and the lowpressure device 108 may not be identical so the control unit 60 may onlyclose off the inline pressure reducer to one of the devices. Forexample, the high pressure device may be a laundry unit with anacceptable steam quality ranging from 80% to 100% while the low pressuredevice 108 is a surgical instrument sterilizer with an acceptable steamquality range of 95% to 100%. In the event that the steam quality fallsto 90%, the laundry unit would continue to operate normally while analarm would sound for the sterilization unit. Alternatively, features atthe pressure reducer directly upstream of the sterilization unit wouldact to close off the sterilization unit. In this example, the there ismore than a 5% difference in the steam quality thresholds at whichalarms sound for the laundry and surgical instrument sterilizer.

The steam analysis system may be an original part of the steam system,or the analysis system may be added after the steam system has beeninstalled. When the analysis system is added to an already existingsteam system, any existing pressure sensors, temperature sensors,pressure drops, data cables, and computer equipment may be utilized toreduce the cost of the steam analysis system.

The steam sterilization system 10 is operated by placing articles in thechamber 32 that is heated by pumping saturated steam from the steamgenerator 50 into the steam region 42, via the first conduit 12. Afterthe steam region 42 is charged, saturated steam is injected into thechamber 32 via the input conduit 14. During a decontamination cycle,sensors 300-600 monitor the steam being provided to the chamber 32. Inthe event that it is determined that the steam does not comply with therequired steam quality, then the control unit 60 may provide an audibleand/or visual indicator to the operator. Furthermore, it may benecessary to take corrective action, including reprocessing the articlesin the chamber. Data collected by the sensors 300-600 duringdecontamination cycles may be stored on a computer readable medium toprovide historical data for verification of appropriate decontaminationprocessing conditions.

At the end of a decontamination cycle, steam is pumped out of thechamber 32 via the outlet conduit 16, and the chamber 32 is evacuated toa pressure below atmospheric pressure to remove moisture from thechamber 32 or on articles therein. Steam leaving the chamber 32 may becondensed, and may drain down to be recycled at the steam generator 50via the water inlet conduit 18 if the chamber is located at a higherposition than the steam generator. If the steam generator is locatedabove the chamber, the condensate may be pumped up to the steamgenerator.

The system controller may continuously calculate the steam quality at aplurality of different locations in the system by utilizing an array ofpressure and temperature monitors. Utilizing data gathered frommonitoring the system and stored data relating to the properties ofsteam mixtures, the system is able to calculate the steam quality. Forexample, if the measured upstream temperature is 143.32° C., themeasured upstream pressure is 200 psi, the measured downstreamtemperature is 121.11° C., and the measured downstream pressure is85.273 psi, then the steam quality may be determined by:

Q=200×P _(U)+143.32×T _(U)+85.273×P _(D)+121.11×T _(D) +K

wherein Q is the steam quality upstream, P_(U) is the upstream pressurefactor, T_(U) is the upstream temperature factor, P_(D) is thedownstream temperature factor, T_(D) is the downstream temperaturefactor, and K is a constant stored on the system controller.

While the principles of the invention have been shown and described inconnection with specific embodiments, it is to be understood that suchembodiments are by way of example and are not limiting. Consequently,variations and modifications commensurate with the above teachings, andwith the skill and knowledge of the relevant art, are within the scopeof the present invention. The embodiments described herein are intendedto illustrate best modes known of practicing the invention and to enableothers skilled in the art to utilize the invention in such, or otherembodiments and with various modifications required by the particularapplication(s) or use(s) of the present invention. It is intended thatthe appended claims be construed to include alternative embodiments tothe extent permitted by the prior art.

1. A method of calculating the quality of a steam mixture flowing from ahigh pressure steam source to a low pressure steam device, the steammixture having an unknown quantity of liquid component, the methodcomprising the steps of: passing the steam mixture from a high pressureregion to a low pressure region through a first inline pressure reducer;passing the steam mixture from the low pressure region to the lowpressure steam device; measuring both the temperature and pressure ofthe steam in both the high pressure region and the low pressure region;and calculating the quality of the steam mixture from the measuredtemperatures and pressures.
 2. The method of claim 1 wherein all of thesteam mixture from the high pressure steam source passes through thefirst inline pressure reducer.
 3. The method of claim 1 wherein steammixture in the high pressure region has a pressure of 50 to 100 psig,and the steam mixture in the low pressure region has a pressure of 25 to35 psig.
 4. The method of claim 1 further comprising issuing an alarm ifthe calculated quality of the steam mixture is below 95%.
 5. The methodof claim 1 further comprising passing the steam mixture from the highpressure region to a medium pressure region through a second inlinepressure reducer; passing the steam mixture from the medium pressureregion to a medium pressure steam device; triggering a first alarm forthe low pressure device when the steam quality falls below a firstthreshold percentage; triggering a second alarm for the medium pressuredevice when the steam quality falls below a second threshold percentage,wherein the first threshold percentage is more than 5% larger than thesecond threshold percentage.
 6. The method of claim 5 wherein the lowpressure device includes a surgical instrument sterilizer.
 7. The methodof claim 1 wherein the temperatures and the pressures are continuouslymonitored, and the steam quality is continuously calculated.
 8. Themethod of claim 1 further comprising the step draining a steamcondensate down from the low pressure device to the high pressure steamgenerator; and heating the steam condensate with the high pressure steamgenerator.
 9. The method of claim 8 wherein the low pressure device isintermittently operated and the low pressure device intermittently drawsthe steam mixture from the low pressure region; while low pressuredevice is inoperative, the first inline pressure reducer blocks the flowof the steam mixture from the high pressure region to the low pressureregion, the temperature and pressure of the steam in both the highpressure region and the low pressure region are continuously measured,and the quality of the steam mixture is continuously calculated.
 10. Asystem for providing multiple pressures of a steam with a known steamquality to a plurality of steam utilizing devices, the systemcomprising: a high pressure steam generator providing a high pressuresteam to a high pressure artery, a first inline pressure reducertransferring the steam from the high pressure artery to a mediumpressure artery at a medium pressure; a first inline pressure adapterconnecting to the high pressure artery, the first inline pressureadapter withdrawing high pressure steam from the high pressure arteryand provide steam at a first pressure to a first device; a second inlinepressure adapter connecting to the medium pressure artery, the secondinline pressure adapter structured to withdraw medium pressure steamfrom the medium pressure artery and provide steam at a second pressureto a second device; a first analysis module flanking the first pressureadapter to continuously monitor the steam quality of the steam providedto the first device, a second analysis module flanking the secondpressure adapter to continuously monitor the steam quality of the steamprovided to the second device, wherein each analysis module includes anupstream inline temperature monitor and an upstream inline pressuremonitor, each monitor located upstream of the flanked adapter, and adownstream inline temperature analyzer and a downstream inline pressureanalyzer, each analyzer located downstream of the flanked adapter. 11.The system of claim 10 wherein the first inline pressure adapterintermittently stops the flow of steam from the high pressure artery tothe first device, and the first analysis module monitors the steamquality of the steam while the flow of steam from the high pressureartery to the first device has been stopped.
 12. The system of claim 10wherein the second analysis module issues an alarm when the monitoredsteam quality is below a higher threshold quality, and the firstanalysis module only issues an alarm when the monitored steam quality isbelow a lower threshold quality.
 13. The system of claim 12 wherein thehigher quality is 95%.
 14. The system of claim 10 wherein the highpressure steam generator, the high pressure artery, the first inlinepressure reducer, the medium pressure artery, the first inline pressureadapter, the first device, the second inline pressure adapter, thesecond device, the first analysis module, and the second analysis moduleare all located within a single building.
 15. The system of claim 14further comprising a first drain line connecting to the first device andthe high pressure steam generator, wherein a steam condensate drainsdown through the drain line from the first device to the high pressuresteam generator.
 16. The system of claim 10 wherein the second device isa surgical instrument sterilizer.
 17. A system for monitoring thesuperheat and the steam quality of a steam delivered to adecontamination machine, the system comprising: an inline pressure dropdevice for providing steam at a reduced pressure and defining a boundarybetween an upstream region and a downstream region; an upstream pressuresensor for producing an upstream pressure signal corresponding to anupstream steam pressure exerted upon the upstream pressure sensor, anupstream heat sensor for producing an upstream temperature signalcorresponding to an upstream steam temperature, a downstream pressuresensor for producing a downstream pressure signal corresponding to adownstream steam pressure exerted upon the upstream pressure sensor, adownstream heat sensor for producing a downstream temperature signalcorresponding to a downstream steam temperature, a data storage devicefor receiving and recording the upstream pressure signal, the upstreamtemperature signal, the downstream pressure signal, and the downstreamtemperature signal, the data storage device including a table offundamental water properties stored on a computer readable medium; aprocessor for determining both the superheat and steam quality of thesteam from the pressure signals, the temperature signals, and the tableof fundamental water properties; a warning device for displaying a firstindicator when the superheat of the steam is beyond a first thresholdvalue, and a second indicator when the steam quality of the steam isbeyond a second threshold value.
 18. A system according to claim 17,further comprising a steam generator, controlled by the processorcontroller, for providing steam to the inline pressure drop device. 19.A system according to claim 17, wherein the processor regulates adesuperheating process.
 20. A system according to claim 17, wherein thesystem intermittently provides steam to the decontamination device andisolates the decontamination device from the steam.
 21. The system ofclaim 20 wherein the system provides the decontamination device withsteam for at least five minutes before the system isolates thedecontamination device from the steam.